Abstract: All primates, including, of course, humans, have evolved to have forward-facing eyes; each eye sees almost the same view of the world. By giving up the view of possible predators approaching from behind, our species gained highly precise stereopsis. The median stereoacuity for college students is 12 (Coutant & Westheimer,1992); it is roughly half this value for practiced subjects (Howard, 1919). In the natural world, what is the use of such precise stereoacuity? Using physical targets, real rods presented in a cluttered environment, I found that binocular estimates are far superior to monocular estimates of depth. Although the rich variety of monocular depth cues is often touted as sufficient for depth perception, the simple geometry of the change in angular subtense with distance shows why stereopsis provides better information about relative depth up to distances of about 15 meters. In addition to providing exquisite information about the relative location of features in our surroundings, stereopsis is important in guiding hand movements, particularly grasp. Even the poor stereopsis found in the periphery of some AMD patients, can be helpful in hand guidance (Verghese et al, 2016). Inspired by this result, we measured the upper limit of stereopsis as a function of eccentricity (Ghahghaei et al, 2017) and found that it changed very gradually from zero to 10 degrees, consistent with Ogles ancient estimate (1954).